The invention relates to a holding apparatus designed to electrostatically hold a component, in particular a silicon wafer. The invention relates also to a method for producing the holding apparatus. Applications of the invention are in the provision of devices or tools for holding components by means of electrostatic forces, in particular for holding semiconductor components, for example silicon wafers.
Holding apparatuses for holding components electrostatically, which are also referred to as electrostatic holding apparatuses, electrostatic clamping apparatuses, electrostatic clamps, ESCs or electrostatic chucks, are known in general. An important application of electrostatic holding apparatuses is in holding silicon wafers in lithographic semiconductor processing, for example in chip production, in which the particular advantages of electrostatic holding, such as the ease of switching of electrostatic holding or clamping forces, a high positioning accuracy and the reliable fixing of silicon wafers, are exploited.
Typically, an electrostatic holding apparatus has a structure having a plurality of plate-type or layer-type elements that perform differing functions (see e.g. U.S. Pat. No. 4,502,094 or US 2013/0308116 A1). At least one plate-type element is equipped with an electrode device, by means of which the electrostatic holding forces are generated. According to US 2013/0308116 A1, the electrode device comprises a plurality of electrodes which are embedded in a multilayer plate-type element. At least one further plate-type element is made of a mechanically stiff ceramic for performing a carrying and cooling function. Furthermore, an electrostatic holding apparatus typically has on its upper side a plurality of projecting upper burls which form a support surface for the silicon wafer.
The conventional electrostatic holding apparatus, for example according to US 2013/0308116 A1, has the following disadvantages. The production of the holding apparatus is complex because of the embedding of the electrodes into a plate-type element. The connecting lines of the electrodes which are required for receiving a clamping voltage must likewise be embedded into the first plate. As a result, the electrostatic holding forces can be distributed inhomogeneously along the support surface and may tend to change over time (aging). The embedded electrodes are at a relatively large distance from the component to be held and therefore require a high clamping voltage. Furthermore, the conventional electrostatic holding apparatus is sensitive to particles. Particles which are approximately as large as or larger than the gap between the component to be held and the underlying dielectric interfere with the planarity considerably and can damage the dielectric. The holding force (clamping pressure) is reduced by the gap caused by particles. Further disadvantages arise because, in most electrostatic holders, the burls are made of a dielectric material. As a result, the heat transfer from the wafer into the temperature-adjusted body of the holder is impaired.
A further problem in the production of the conventional holding apparatus is that the plate-type elements have to be produced in succession in terms of time, the mechanically stiff plate-type element being produced first and the plate-type element with the embedded electrodes then being composed. The production time is lengthened as a result, and flexible matching of the holding apparatus to the requirements of a specific application is made more difficult.
The mentioned disadvantages occur not only in the case of electrostatic holding apparatuses for silicon wafers, but also in the case of holding apparatuses having embedded electrodes for other components, such as, for example, for glass plates having a transparent electrode (ITO), which form AMLCD substrates.